I would first of all tell them to get active on campus. Find a club you can be excited about because I believe it is a very important part of college. It introduces you to more people (important because many freshman don't know many people coming in), as well as provides for leadership opportunities to build resumes. I would also encourage them to start the semester right and search out for academic help if you need it. There are help sessions and office hours that they don't necessarily understand are there to help them. Many haven't needed help in high school, but they shouldn't be afraid to ask for help when college is harder. I would also encourage them to build a good resume and get a Linkedin since these will be vital as they go through school. I would also make sure to encourage them to try new opportunities because college is largely about the opportunity to experience different cultures and ideas.